Conventional window and door manufacturers have commonly used wood and metal components in forming structural members. Commonly, residential windows are manufactured from milled wood products or extruded aluminum parts that are assembled with glass to form typically double hung or casement units. Wood windows while structurally sound, useful and well adapted for use in many residential installations, can deteriorate under certain circumstances. Wood windows also require painting and other periodic maintenance. Wooden windows also suffer from cost problems related to the availability of suitable wood for construction. Clear wood products are slowly becoming more scarce and are becoming more expensive as demand increases. While metal components are often combined with glass and formed into single unit sliding windows, metal windows typically suffer from substantial energy loss during temperature extremes of heat or cold.
Extruded thermoplastic materials have also been used as non-structural components in window and door manufacture. Filled and unfilled thermoplastics have been extruded into useful seals, trim, weather-stripping, coatings and other window construction components. Thermoplastic materials such as polyvinyl chloride have been combined with wood members in manufacturing PERMASHIELD.RTM. brand windows manufactured by Andersen Corporation for many years. The technology disclosed in Zanini, U.S. Pat. Nos. 2,926,729 and 3,432,883, have been utilized in the manufacturing of plastic coverings or envelopes on wooden or other structural members. Generally, the cladding or coating technology used in making PERMASHIELD.RTM. windows involves extruding a separate thin polyvinyl chloride outer layer or envelope surrounding a wooden structural member.
Polyvinyl chloride has been combined with wood fiber to make extruded materials. Such materials have successfully been used in the form of a structural member that is a direct replacement for wood. These extruded materials have sufficient modulus, compressive strength, coefficient of thermal expansion to match wood to produce a direct replacement material. Typical composite materials have achieved a modulus greater than about 500,000 psi (preferably between 600,000 and 1,500,000 psi) acceptable COOT, tensile strength, compressive strength, etc. to be useful. Deaner et al., U.S. Pat. Nos. 5,406,768, 5,441,801, 5,486,553, 5,497,594, 5,518,677, 5,539,027 and 5,695,874 and U.S. Ser. Nos. 08/543,959 (application pending, filed 17 Oct. 1995) and 08/587,828 (application abandoned) disclose a PVC/wood fiber composite that can be used as a high strength material in a structural member. This PVC/fiber composite has utility in many window and door applications.
A substantial and continuing need exists to provide a improved composite material that can be made of thermoplastic polymer and wood fiber. The composite can be made with an optional, intentional recycle of a waste stream. A further need exists for a composite material that can be extruded into a shape that is a direct substitute for the equivalent milled shape in a wooden or metal structural member. A thermoplastic with fiber compatibility, good thermal properties and good structural or mechanical properties is required. This need also requires a composite with a coefficient of thermal expansion that approximates wood, that can be extruded into reproducible stable dimensions, a high modulus, a high tensile strength, a high compressive strength, a low thermal transmission rate, an improved resistance to insect attack and rot while in use and a hardness and rigidity that permits sawing, milling, and fastening retention comparable to wood members. Still further need exists to optimize the structural properties of the material and to increase productivity without reducing composite structural properties.